The invention relates to a compressed air supply system for a utility vehicle, having an air dryer unit with a filter unit, with an electrically activatable valve unit and with a pneumatically activatable blow-off valve unit, a compressor which supplies compressed air to the air dryer unit via a feed line, a multi-circuit protective valve unit which draws compressed air from the air dryer unit, and an electrically activatable compressor coupling switching valve unit.
The invention also relates to a method for operating a compressed air supply system for a utility vehicle.
Utility vehicles having pneumatic components require a compressed air supply system. The compressed air is generally fed by a compressor into an air treatment system where the air which is introduced is cleaned in a filter unit before then finally being supplied via a multi-circuit protective valve for use, for example by the brake system of the utility vehicle.
After certain feed quantities are reached or after certain periods of time have elapsed, it is necessary to clean the filter unit. For this purpose, valves are connected within the air treatment system in such a way that compressed air from storage tanks, either the storage tanks of the service brake circuit or one or more storage tanks provided especially for the purpose, flows in the reverse direction through the filter unit, before then being allowed to flow, laden with moisture and foreign particles, out of the filter unit and into the atmosphere. During said regeneration phases, the compressor is generally shut off or placed into an idle phase.
A disadvantage of said regeneration phases is the compressed air consumption. In particular, the compressed air which is present in the feed line between the compressor and the filter unit is lost unnecessarily during the regeneration if suitable countermeasures are not implemented. To prevent the loss of said compressed air, it has already been proposed to shut off the feed line between the compressor and the filter unit during the regeneration phases. Such a shut-off is also referred to as “turbo cut-off” since the compressor often extracts compressed air from the turbo system of the utility vehicle, such that the shut-off of said feed line keeps an air loss in the turbocharger low. It is in particular also possible for the overrun operation of the utility vehicle to be utilized for the recovery of compressed air, while the compressor is simultaneously feeding air. This results in an energy saving.
In conventional systems, provision is now made for a regeneration of the filter unit to be carried out in every idle phase of the compressor. In practice, however, this frequently leads to an over-regeneration of the filter unit and therefore to an excessive loss of compressed air, such that the positive effect of the compressor deactivation is ultimately overcompensated for in a negative way as a result of the loss of compressed air. Furthermore, the benefit of the overrun phases of the motor vehicle is not always without its problems, since it is also the case here that shift processes, in particular those which involve the switching of the compressor, lead to air losses which sometimes again nullify the energy saving obtained by the utilization of the overrun phases.
Compressed air supply systems can be divided into different classes with regard to their degree of integration. Here, purely pneumatic systems and electropneumatic systems which are fitted with their own control and regulating electronics represent the boundaries of the spectrum of integration. In the present connection, the focus is on systems referred to as semi-dryers, that is to say systems which have an air dryer and electrically and pneumatically activatable valves within a unit but which are activated by an external electronic control unit. Although this partially opposes the basic demand for an ever greater degree of integration, this does however offer advantages with regard to the arrangement of the compressed air supply system in the utility vehicle, since the components can be arranged in a distributed fashion taking into consideration the available installation space. The basic considerations regarding energy saving during the generation of compressed air apply here to the same extent as to fully integrated systems.
The object on which the invention is based is that of coordinating the deactivation of the compressor and the regeneration of the compressed air supply system in the most economic way possible.
The invention builds on the generic compressed air supply system in that an electronic control unit is provided which controls and/or regulates functions of the air dryer unit and of the compressor coupling switching valve unit. The electronic control unit may consequently control all the functions associated with the supply of compressed air and in particular with the saving of compressed air. This relates firstly to the core functions of the air dryer unit, specifically the air treatment, the possibility of regeneration and a pressure regulating function. The feed phases and non-feed phases of the compressed air supply system may be made dependent on numerous parameters, the values of all of which are available to the electronic control unit. It is consequently possible to provide optimized operating processes.
It is expediently provided that the electronic control unit is suitable for placing the compressed air supply system into an energy saving operating state in which the compressor coupling switching valve unit separates the compressor coupling. To obtain an energy saving, therefore, the compressor is no longer driven.
It may then be provided in particular that the electronic control unit is suitable for placing the compressed air supply system into a regeneration operating state in which the compressor coupling switching valve unit separates the compressor coupling, the electrically activatable valve unit is activated and the pneumatically activatable blow-off valve unit opens a blow-off line. The energy saving may thus be maintained even during the regeneration phase of the compressed air supply system.
The invention is expediently refined in that a further electrically activatable valve unit is provided, and in that a feed line shut-off valve unit is provided which can be pneumatically activated by the further electrically activatable valve unit. With regard to the saving of energy, it is possible for a feed line shut-off valve to be pneumatically actuated indirectly by means of the electrically activatable valve units in the air dryer unit, with said actuation being adapted to the presence of a feed phase and/or a non-feed phase of a compressor which is coupled to an internal combustion engine by means of a coupling.
It may also be provided that the feed line shut-off valve unit closes the feed line in the energy saving operating state. The closure of the feed line serves to prevent the compressed air which is situated in the feed line from being lost.
It is likewise expedient for the feed line shut-off valve unit to close the feed line in the regeneration operating state. The saving of the compressed air which is situated in the feed line may thus be maintained even during the regeneration phase of the compressed air supply system.
It may also be provided that the electronic control unit is suitable for placing the compressed air supply system into a feed air renewal operating state in which the compressor coupling is closed, the feed line shut-off valve unit opens the feed line and the pneumatically activatable blow-off valve unit opens a blow-off line. Such a process is expedient for preventing freezing of the feed line.
It is therefore particularly advantageous that the feed air renewal operating state can be assumed in particular when a temperature sensor which is connected to the electronic controller provides a value which is characteristic of the external temperature which lies below a threshold value.
It may also be provided that the blow-off valve unit can be pneumatically activated by the electrically activatable valve unit. In this way, the feed line shut-off valve unit can be activated in a targeted fashion without influencing the system in any other way, while the blow-off valve unit is opened whenever the second electrically activatable valve unit is supplied with current. Since the second electrically activatable valve unit is supplied with current in particular in order to carry out a regeneration of the air dryer unit, and since it is necessary here to open the blow-off valve in any case, this is a simple variant in terms of circuitry. It should however be taken into consideration that, if the compressed air in the feed line is to be renewed, it is likewise necessary to open the blow-off valve. At least a brief regeneration of the filter unit will then occur even if this is possibly not required. It is evident that both activation variants of the blow-off valve unit, that is to say either by means of the first electrically activatable valve or by means of the second electrically activatable valve, have advantages and disadvantages, wherein one or the other variant will be preferable depending on the physical application.
It may also be provided that the blow-off valve unit can be pneumatically activated by the further electrically activatable valve unit. The blow-off valve unit is therefore activated by the same electrically activatable valve as the feed line shut-off valve unit. Consequently, the feed line shut-off valve unit is always closed when the blow-off valve unit is opened. This ensures that a loss of the feed line volume is prevented in any case, but makes an increase in system pressure necessary if the feed line volume is to be exchanged for the purpose of preventing freezing.
It may expediently be provided that the blow-off valve unit has a control piston which, during the ventilation of a control chamber, opens a blow-off valve, with a 2/2-way valve function additionally being provided for blocking and opening up a regeneration air path. If the switching of the blow-off valve by the circuit logic is always coupled to the execution of a regeneration, such an integrated design of a valve with a plurality of functions is expedient, wherein all the functions may be realized by aerating a single control chamber.
The invention builds on the generic method in that the functions of the air dryer unit and of the compressor coupling switching valve unit are controlled and/or regulated by means of an electronic control unit. In this way, the advantages and peculiarities of the compressed air supply system according to the invention are also realized within the context of a method. This also applies to the particularly preferred embodiments of the method according to the invention as specified below.
The method is expediently refined in that the electronic control unit places the compressed air supply system into an energy saving operating state in which the compressor coupling switching valve unit separates the compressor coupling.
It may be provided in particular that the electronic control unit places the compressed air supply system into a regeneration operating state in which the compressor coupling switching valve unit separates the compressor coupling, the second electrically activatable valve unit is activated and the pneumatically activatable blow-off valve unit opens a blow-off line.
The method according to the invention may be realized in a particularly expedient fashion in that a further electrically activatable valve unit is provided, and in that a feed line shut-off valve unit is provided which can be pneumatically activated by the further electrically activatable valve unit. It may then be provided that the feed line shut-off valve unit closes the feed line in the energy saving operating state. It is also possible for the feed line shut-off valve unit to close the feed line in the regeneration operating state.
The method according to the invention is in particular then expediently refined in that the electronic control unit places the compressed air supply system into a feed air renewal operating state in which the compressor coupling is closed, the feed line shut-off valve unit opens the feed line and the pneumatically activatable blow-off valve unit opens a blow-off line.
In this connection, it is advantageous for the feed air renewal operating state to be assumed in particular when a temperature sensor which is connected to the electronic controller provides a value which is characteristic of the external temperature which lies below a threshold value.
According to one variant of the method according to the invention, it may be provided that the blow-off valve unit is pneumatically activated by the electrically activatable valve unit.
According to another variant, it is also possible for the blow-off valve unit to be pneumatically activated by the further electrically activatable valve unit.
It is also provided that the electronic controller controls the transitions between the feed state and the energy saving operating state on the basis of a predefined activation pressure threshold and a predefined deactivation pressure threshold, with the deactivation pressure threshold corresponding to a greater pressure than the activation pressure threshold. The presence of a feed phase or a non-feed phase of compressed air is thus made dependent on the present system pressure.
It is in particular provided that the electronic control unit places the compressed air supply system into a feed state if a pressure measured at the compressed-air consumer side falls below an activation pressure threshold.
It is also expedient for the electronic control unit to place the compressed air supply system into the energy saving operating state if a pressure measured at the compressed-air consumer side exceeds a deactivation pressure threshold.
It is particularly advantageous for the electronic control unit to place the compressed air supply system into a feed state if the utility vehicle is in an overrun operating phase and if a pressure measured at the compressed-air consumer side lies between an activation pressure threshold and a deactivation pressure threshold. It is thus possible for the compressed air supply device according to the invention to be placed into a feed state even when the activation pressure threshold has not yet been reached, specifically when the vehicle is in an overrun phase. In this way, the energy which is converted into heat energy, and therefore made useless, mostly as a result of braking operations during the overrun phase is converted into an increased compressed air reserve. It is particularly expedient for the additional feed of compressed air above the activation pressure threshold to be carried out when an imminent increased compressed air demand is expected.
It is particularly preferable for the deactivation pressure threshold to be increased if the utility vehicle is in an overrun operating phase. The increase of the deactivation pressure threshold may be expedient both when the compressor has switched into the feed phase on account of the activation pressure threshold being undershot, and when the feed phase has been commenced without the activation threshold being undershot.
The invention will now be explained by way of example below with reference to the appended drawings on the basis of particularly preferred embodiments. In the drawings: